unix fold utility

Hello again! lol. I have to create a fold utility program as our final project (we had 3 choices). I am having trouble getting started on it. I will post a link to the description of what the fold command is supposed to do.

http://www.conestogac.on.ca/~set/cou..._fold_2008.htm

This is due on Tuesday btw.

UPDATE: So far I have this...

Code:

---

#include <stdio.h>

int main(int argc, char *argv[])
{
        FILE *inputFile; //pointer to a file//

        if (argv[1] == '-s')
        {
        // Fold line after the last blank character within the first width column positions.
        // If there is no such character, fold anyway.
        }

        if (argv[2] == '-w' && argv[3] == /* width variable here*/)
        {
        // Specify a line width to use instead of the default 80 columns.
        }

        inputFile = fopen(argv[4], "r"); //open a file for reading//

        if (inputFile = fopen(argv[4], "r") == NULL)
        {
                printf("Cannot open file for reading.\n"); //display error if file is not found//
                return -1;
        }
       
        if (inputFile = fopen(argv[4], "r") != NULL)
        {
                return -2;
        }

        //other code here//

        return 0;
}

---

I guess that separate functions would be a good idea to use for each command line argument?

Sketch out a rough program and someone from the msg board is sure to help.

thanks, this board indeed need to keep track of your last assignments ;)
I may have missed the blog-related section in the FAQ...

Can I ask if this is your major and you started in September?

I don't think that either of your command line switches deserve their own function; after all, for -s you should probably just do word_wrap = true and for -w you would just do columns = <whatever>. You do need to not assume that they will come in that order, or that both of them will be given. In other words, you need to loop through each command line argument in turn, and process each. Note also that you cannot assume a space between -w and 75 (or whatever number), so assuming that they are in separate argv's won't work. You also shouldn't try to open your input file three times. And what's with the return -2? (Oh, and for that matter, what's with the return -1? Look at your spec sheet again.)

And technically, the error message when you can not open the file is incorrect.

--
Mats

This looks more to be a switch/case assignment with some strlen() usage thrown in. I would review how getopt() works.

I believe this to be a foolproof and completely optimized way of parsing your particular options:

Code:

---

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void wrong () {
        puts("Usage: fold [-s] [-w width] file ...");
        exit (-2);
}

int parse_w (char *arg) {
        int i, retv;
        if (sscanf(arg,"&#37;d",&retv)!=1) wrong();
        return retv;       
}

int main (int argc, char *argv[]) {
        int i, len, sflag=0, width=80;
        FILE *fstRO;
        for (i=1;i<argc;i++) {
                if (strcmp(argv[i],"-s")==0) {sflag=1;continue;}
                if (strncmp(argv[i],"-w",2)==0) {
                        if (strlen(argv[i])>2) {
                                if (sscanf(argv[i], "-w%d",&width)!=1) wrong();
                                continue;}
                        else if (i==argc-1) wrong();
                        width=parse_w(argv[i+1]);
                        i++; continue;
                }
                break;
        }
        if (!(fstRO=fopen(argv[i],"r"))) {
                puts("File not openable");
                return -1;}
        printf("%s opened read-only\n",argv[i]);
        if (sflag==1) puts("-s set");
        printf("width set to %d\n",width);
        fclose(fstRO);
        return 0;
}

---

edit: except it doesn't parse the filename...oh well
edit2: okay now it does

That looks like it should be right for the switches, if not the filenames, of course. I think the usual idiom is a switch on the second letter of the argument; for two possible arguments I don't know that there's a performance hit either way, but the switch may make it a little easier to tell "illegal option" from "first filename".

Quote:

---

Originally Posted by tabstop

That looks like it should be right for the switches, if not the filenames, of course. I think the usual idiom is a switch on the second letter of the argument; for two possible arguments I don't know that there's a performance hit either way, but the switch may make it a little easier to tell "illegal option" from "first filename".

---

Our paths crossed, I edited it to get the filename. Re: what you are saying about optimization, so

Code:

---


if (argv[i][0]=='-') switch (argv[i][1]) {
            case ('s'):
  //...etc

---

I guess this could save some strcmp

Cripes, why reinvent the wheel?? Use getopt!

Quote:

---

Originally Posted by rags_to_riches

Cripes, why reinvent the wheel?? Use getopt!

---

You're making a pretty big assumption, there, that I'm not sure is warranted.

You know what, you're right...I did jump to a big ol' conclusion, didn't I?

Sorry.

Quote:

---

Originally Posted by MK27

Can I ask if this is your major and you started in September?

---

I did start in September. I am having some trouble focusing though. :(

Before handing over the assignment the teacher must have covered how to do option processing. Hard to believe she or he would just pull it out of the hat.

Quote:

---

Originally Posted by itCbitC

Before handing over this assignment the teacher must have covered how to do option processing in class. Hard to believe that she or he would just pull it out of the hat.

---

Why? I'm not a computer science prof yet, but it seems like something where you should be able to spot the angles after a few months. I wouldn't want my students to just sleep thru their final project -- I'd have such a big hat they'd love me forever

Quote:

---

Originally Posted by MK27

I believe this to be a foolproof and completely optimized way of parsing your particular options:

Code:

---

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

void wrong () {
        puts("Usage: fold [-s] [-w width] file ...");
        exit (-2);
}

int parse_w (char *arg) {
        int i, retv;
        if (sscanf(arg,"%d",&retv)!=1) wrong();
        return retv;       
}

int main (int argc, char *argv[]) {
        int i, len, sflag=0, width=80;
        FILE *fstRO;
        for (i=1;i<argc;i++) {
                if (strcmp(argv[i],"-s")==0) {sflag=1;continue;}
                if (strncmp(argv[i],"-w",2)==0) {
                        if (strlen(argv[i])>2) {
                                if (sscanf(argv[i], "-w%d",&width)!=1) wrong();
                                continue;}
                        else if (i==argc-1) wrong();
                        width=parse_w(argv[i+1]);
                        i++; continue;
                }
                break;
        }
        if (!(fstRO=fopen(argv[i],"r"))) {
                puts("File not openable");
                return -1;}
        printf("%s opened read-only\n",argv[i]);
        if (sflag==1) puts("-s set");
        printf("width set to %d\n",width);
        fclose(fstRO);
        return 0;
}

---

edit: except it doesn't parse the filename...oh well
edit2: okay now it does

---

what is int retv in the top function?

If I try to use this as a guide, i'll be pretty lost.

parse_w makes sure the value passed to it is an integer, and returns that integer if so. retv is the integer variable into which the string argument is parsed and which is returned to the caller.

Quote:

---

Originally Posted by MK27

Why? I'm not a computer science prof yet, but it seems like something where you should be able to spot the angles after a few months. I wouldn't want my students to just sleep thru their final project -- I'd have such a big hat they'd love me forever

---

With a big hat you would even be able to pull off a bunny :D which is in contrast to what a teacher ought to do; perhaps a pointer or a nudge in the right direction. I was curious if something similar had been covered in class. However I would go with something along the lines that tabstop suggested or look at the man page of getopt() to get an idea of how to go about this.

Quote:

---

Originally Posted by itCbitC

With a big hat you would even be able to pull off a bunny :D which is in contrast to what a teacher ought to do; perhaps a pointer or a nudge in the right direction. I was curious if something similar had been covered in class. However I would go with something along the lines that tabstop suggested or look at the man page of getopt() to get an idea of how to go about this.

---

Hmm...there is a spectrum in that attitude. At one end, the prof could issue a handout and tell everyone that this is their completed assignment they are about to turn in, and explain in detail how they managed to do it. At the other, s/he could just demand an undescribed assignment, then wait until after the assignments had been handed in to explain what was suppose to be done, which I would agree that's not so helpful and could lead someone in just about any direction with very little clue about what the right one might be.

tabstop's suggestion about using switch is definately the thing here. From looking at the assignment, I would say the most complicated part is actually dealing with the options. Since you should be able to optimize beyond what getopts will give you, doing that instead might make a big difference to the whole.

All I have to say is :

http://www.conestogac.on.ca/registra...dishonesty.jsp

Do your assignments yourself. First year is NOTHING compared to the stuff to come. If you're having THAT much trouble I would consider switching to another program because it doesn't get any easier.